What's the longest you've ever used a particular computer, without giving/putting it away, or replacing the motherboard? It doesn't have to be your newest/primary computer.
For me, it's the desktop that I upgraded from Athlon X2 to Core 2 Duo in the summer of 2008. I still use it to test out new games and have recently upgraded the CPU to Core 2 Quad and added 2 more GB of RAM.
A truly prophetic sig...